This subject matter disclosed herein relates generally to imaging systems, and more particularly, to apertures for an x-ray collimator.
Non-invasive imaging broadly encompasses techniques for generating images of the internal structures or regions of a person or object. One such imaging technique is known as x-ray computed tomography (CT). CT imaging systems measure the attenuation of x-ray beams that pass through the object from numerous angles (often referred to as projection data). Based upon these measurements, a computer is able to process and reconstruct images of the portions of the object responsible for the radiation attenuation.
Collimators are used to filter a stream of rays from a source (such as an x-ray tube) so that the rays traveling in a desired direction or directions are allowed to pass through. The collimator may be made from a material that substantially blocks x-rays, with an aperture provided to allow a portion of the x-ray beams to pass through. For example, a system may include a source and a detector. For good image reconstruction, it is desirable that all or a given portion of a detector be uniformly covered by x-rays from the source.
Certain CT systems use detectors that are generally rectangular in shape, but that curve with respect to a plane that is transverse to the x-ray beam. Use of a substantially planar collimator with a generally rectangular aperture profile to shape an x-ray beam to project on such a curved detector can result in undesirable beam projection coverage of the detector. The beam projection through the flat aperture results in a distortion (a different shape than that of the aperture) on a curved detector. This distortion reduces the dose efficiency of the system. This additional portion of the beam extending beyond the usable (or desired to be used) portion of the detector results in a patient being exposed to un-used x-rays, or an additional dose.
Certain known CT systems have attempted to address this issue in various ways. For example, collimators that are curved along a length thereof instead of being substantially planar have been employed. These designs, however take up significantly more space than a substantially planar aperture, with space often being at a premium in CT systems (for example, space occupied by a collimator can be a limiting factor on size of bore). Also, for example, apertures with linear ramps extending from edge to center have been employed. While these linearly ramped apertures reduce the overdose when compared to rectilinear aperture shapes, linearly ramped apertures still result in un-used x-ray beam portions.
Thus, presently known collimators occupy too much space, and/or result in an undesired overdose of x-ray exposure, and/or limit or inhibit functionality.